Papermaking fabrics are woven in any number of weave patterns to include patterns for single layer and multi-layer fabrics. Normally, these fabrics are woven endless, cut to length, and a joining seam is formed on each end.
Always of primary importance with papermaking fabrics is wearability, uniform permeability, and evenness or smoothness of the paper sheet support surface. Good wearability produces longer run times and therefore more economy. Uniform permeability allows for even drying which produces a consistent paper sheet. Finally, an even or smooth support surface prevents marks from being formed on the paper product.
Joining seams, while always presenting somewhat of a problem in allowing the papermaking fabric to retain the above characteristics, the problem has not been unsurmountable in most instances. U.S. Pat. Nos. 4,026,331; 4,883,096; and 4,976,293 show various techniques employed to form satisfactory seams in single-ply forming fabrics. Because these fabrics are single-ply, the solutions taught do not necessarily apply to multi-ply fabrics.
U.S. Pat. Nos. 4,186,780; 4,286,631; 4,438,789; and 4,469,142 disclose various solutions to forming joining seams for use with multi-ply fabrics. The basic problem exists because the warp yarns are heat-set after weaving which results in their retaining the crimp structure of the woven fabric. In multi-layer fabrics, this is not a problem as long as the weave is balanced. U.S. Pat. Nos. 4,469,142; 4,286,631; and 4,136,780 show such an even weave structure. Here, using '142 as illustrative, floats 62, 66 of equal size are formed on each fabric face. When forming the seaming loop by weaving back the warp yarns, the surface on which float 62 or 66 appears, is of no great consequence as they are evenly configurated. A smooth, evenly porous seam area is formed.
When forming a seam with an uneven weave, as shown in U.S. Pat. No. 4,438,789, the circumstances are different. The floats appearing on the top surface are of a different length than those appearing on the lower surface. Here, the solution was to disregard the crimp configuration of the warp and to weave them back regardless. This solution produces a rough surface at the seam which marks the paper sheet and also produces uneven permeability.
Another solution is to not turn back the warp until it will properly match up. This solution produces an excessively large pintle receiving loop which allow excessive open area. This arrangement also requires a large pintle which causes the looped warp to extend above the plane of the fabric which produces excess wear.
The object of the present invention is to overcome the drawbacks of the prior seam structures as noted above.
Another object of the invention is to provide, in multi-layer fabrics having uneven weaves, a loop size which fittingly accommodates a small diameter pintle.
Another object of the invention is to provide a smooth support surface in the area of the seam.
Another object of the invention is to maintain a consistent permeability profile throughout the fabric body.
Another object of the invention is to maintain a low profile in the seam so as to reduce wear of the fabric and marking of the paper sheet.